Hi, welcome to the forum. Glad you joined.
I'm not exactly sure what you are asking, are you asking about healthy or productivity? And I'm not sure how you are raising yours. Do they forage for a lot of what they eat or are you providing everything they eat? Or the way I raised them, somewhere in the middle? Are you asking what you should be planting to feed them?
An appropriate commercial chicken feed should provide everything they need to be healthy and productive in balanced amounts of essential nutrients. Here in the States the Analysis is on the label, that tells you the percent of essential nutrients provided. The significant differences are calcium and protein. Hens that are laying eggs need about 4% of their diet to be calcium, which is used for egg shells. All other chickens need about 1% calcium for growth and body maintenance. Too much calcium can be harmful, especially to growing chicks. So getting the right calcium level for your chickens is important. If your egg shells are hard they are getting enough. The other important component is proteins. I can buy chicken feed with protein levels from 15% to 20%, with even higher percent for other types of fowl. If you are raising them for meat the more protein they eat the faster they'll grow. If you are interested more in eggs they don't need that much protein to be healthy and productive.
If you are providing them commercial feeds and that is most of what they eat, the general rule of thumb is that anything in addition should be no more than 10% of their overall diet. That way the commercial feed still provides enough of essential nutrients that they keep a balanced diet.
If chickens forage for most of what they eat you have lost your control over a balanced diet, they have to manage that. And they are pretty good at it. One thing to watch is their egg shells. They can find a lot of calcium in nature from the plants they eat, the creepy crawlies they catch, and if your native soil is limestone from the small rocks they eat. As long as the egg shells are firm they are finding enough calcium somewhere. If you have thin or soft egg shells you might need to offer supplemental calcium. To a large extent chickens seem to know what they need nutritionally as long as hey have a variety of things to forage on. They developed to feed themselves from nature to start with, before we domesticated them.
Trying to grow things that will be their main diet is more challenging to maintain a balanced diet. They can eat just about anything you can: meat, fruit, or vegetables. There are exceptions. Uncooked dried beans contain a substance that can harm them if they eat a volume of them. Avocado can be harmful. stay away from it with chickens. Potatoes are OK for them unless it has been exposed to the sun and has turned green. The green indicates it has developed a harmful component, but you should not be eating green potatoes either. These are the ones I avoid. I don't worry about anything else as long as it is fed in moderation.
One thing I like to do is to give them access to a compost pile. They will keep it turned for you with their scratching and deposit poop that is great for composting. I toss in table scraps, excess stuff from the garden, and all kinds of green stuff. They pick through it for bits of what you toss in there plus anything living in there they can find. And you get tremendous compost for your garden.
What specific crops should you plant? As I said, they can eat practically anything you can. One that I really like is sunflowers for the seeds, but in moderation. Sunflower seeds are pretty high in protein but also in oil, which means fat. Fat is a essential ingredient, about 1/3 of their egg yolks are fat. The oil in sunflower seeds helps make their feathers really shiny and soft. That's a trick people that show chickens use, feed them a little oil to make the feathers really pretty, but in moderation. Too much oil is not good for them.
I'd consider planting green leafy vegetables, especially members of the brassica family. Those are high in many nutrients and they tend to turn the yolks a darker yellow. That doesn't mean the eggs are more nutritious but many people find the darker yolks to be prettier. Commercial feed operations often add marigold petals to their Layer feeds to color the egg yolks. Other flower petals can work for that.
Any grains are good. I don't know what grains you grow there. Grains are grass seeds of some type with a concentration of nutrients. So if you are trying to grow most of their feeds grains are probably a good choice.
I can't think of anything else I'd specifically plant for chickens. Mine really like berries. One of the funniest things I've seen was a grown hen standing under a grape vine and jumping up a couple of feet to pick off grapes. I have several different fruit trees that they eat any fallen fruit. They get the benefit of these but I planted them for me.
I know this is long and rambling. I've tried to touch on several different points as I'm not exactly sure what your plans are. The main thing is that they can eat practically anything you can but try to feed any one component in moderation to maintain a balanced diet.